All Questions

2
votes
1answer
46 views

How to select salt an IKM for HKDF

I have an application where I need to combine a Diffie-Hellman shared secret, with a user's password and derive a key. I'm investigating the possibility of using HKDF to as follows Initial Keying ...
3
votes
1answer
46 views

Question about degree of regularity

I have been reading some papers on cryptography based on multivariate systems and I have a question. How does one relate the difficulty of calculating Gröbner basis (GB) of a multivariate system with ...
5
votes
0answers
45 views

Does there exist trapdoor permutation from lattices?

It seems that the lattice functions are either surjective (SIS) or injective (LWE), due to the error that is basically intended to destroy the structure and provide security. I was wondering whether ...
2
votes
2answers
130 views

What is a good AES mode to use on file encryption?

I'm new to encryption and cryptography, I was wondering if there is a good or best suited AES mode for file encryption (Planning on zipping a folder and encrypt it as a file). If there is, how complex ...
1
vote
2answers
56 views

How many keys in a Hybrid Cryptosystem?

If symmetric cryptosystems have $C^2_n$ keys, and asymmetric systems have $2n$ keys, how many does a hybrid system have? This was in an online quiz from school Company A is considering to adopt ...
1
vote
1answer
52 views

Decrypt simple CBC with XOR

I have searched and my problem is exactly the same as shown here: Decrypt simple CBC message with known IV using XOR encryption However, when I implement the solution it doesn't work, neither does ...
2
votes
2answers
36 views

Why is Blakley secret sharing in finite space?

The paper says it requires a finite space. I wonder what the reason is, since from my understanding it should be perfectly fine to use the "normal" infinite space. So why does Blakley use a finite ...
1
vote
0answers
43 views

Need tips on how to break Fiat-Shamir sigma-protocol (programming challenge)

I'm completely stuck on an university programming challenge and I need some tips to get me out of the valley I'm in, you don't need to give the full answer if you do not wish to. What we have: Fiat ...
16
votes
2answers
4k views

What makes SHA256 secure?

For example, RSA relies on a mathematically hard problem, factoring, while ECDSA or similar rely on discrete logarithm problem. What makes SHA256 and similar hash functions, of the same family, ...
0
votes
0answers
28 views

Develop application using Hyperledger Fabric Java SDK [closed]

I'm modifying an application which uses RSA keys to encrypt and decrypt symmetric keys (which are used to encrypt files). I'm trying to substitute this feature of the central server with the ...
5
votes
2answers
96 views

Is there any hash function that relies on integer exponentiation instead of XOR?

I'm trying to implement a hash function in an esoteric language that has no 32-bit or 64-bit operations. Keccak, for example, is too slow in that language. I'd need a design that minimizes the number ...
2
votes
2answers
61 views

Search Over Encrypted Data

I'm doing a research about how to search over encrypted data as the title said. And, I saw cryptDB used a cryptographic scheme from Song et.al's article Practical Techniques for Searches on Encrypted ...
0
votes
0answers
69 views

Identification of RF hash algorithm [migrated]

I have an unbranded LED lamp with a remote control. I would like to reverse the protocol of the remote but unfortunately I can't create my own packages. The frequency of the remote transceiver is 2....
-1
votes
0answers
31 views

AES-CTR mode using different key's generated trough PBKDF2 in case at least two IVs repeat

Supposed that a client has AES-128 bit randomly generated static key The client is using a PBKDF2 in order to to generate a vector(list) of keys i.e. target keys to leverage will be located ...
2
votes
1answer
27 views

Is it acceptable to add a setup algorithm in the public key encryption?

I saw in the paper How to Use a Short Basis: Trapdoors for Hard Lattices and New Cryptographic Constructions at page 29 that key generation algorithm of PKE can use a common random matrix $A$. Is it ...
0
votes
0answers
22 views

Diffie-Hellman Groups 20 vs 24 [duplicate]

Which encryption under DH has greater Encryption, it's said that the higher the number in DH the greater the encryption but I would like to verify this further. Does Anyone have inputs on this? or ...
2
votes
1answer
60 views

How to make the interactive Schnorr identification protocol become non-interactive

I am reading about ZKP and I found this interesting question about changing this protocol from interactive Schnorr identification protocol to non-interactive and I need help in solving it : Peggy (...
3
votes
1answer
85 views

Generating RSA signature, by manipulating shorter message signatures?

Given a server that can return me RSA sign for any plaintext shorter or equal length of the given plaintext (excluding the given plaintext), how can I fraud/get the sign of the given? $$sign = M^{d} \...
2
votes
1answer
32 views

Using PKCS #11 Certificate Objects for Verification

What is the proper way to use the public key contained in a X.509 certificate with PKCS #11? ...
0
votes
0answers
34 views

How to get unknown constants from linear congruential generator

I need to crack this linear congruential generator. I have $$X_{n+1}=a⋅X_n +b \pmod m$$ I know: $m=31,X_3=30,X_4=19,X_5=26$ How can I find $a,b$ and $X_0$? I have got already the following ...
0
votes
0answers
30 views

How to decrypt a simple substitution cipher where space is also encrypted by a character

I am trying to decrypt a text data encrypted with a simple substitution method with 2 steps. First, shift the alphabet of the source text by a few characters. For example, if we shift by 2 characters,...
6
votes
0answers
85 views

GCM with reversed poly

These slides talk about how GCM can be sped up if one uses $x^{128}+x^{127}+x^{126}+x^{121}+1$ as the reduction polynomial instead of $x^{128}+x^7+x^2+x^1+1$. When one is doing that one needs to ...
3
votes
1answer
109 views

How is Blakley's Secret Sharing Scheme perfect?

Currently, I am trying to understand Blakley's secret sharing scheme. However, there seem to be multiple descriptions of it, which are very different from another, but everyone states that the scheme ...
2
votes
2answers
61 views

Random Self-reducibility in Discrete Log

I understand what Random Self-reducibility means and how it is used in the Discrete Log. What is not clear is how does it show that DL is hard in the average case. The probability of success of an ...
11
votes
1answer
122 views

Why is $e=0$ allowed in Schnorr signatures?

In a Schnorr signature (Wikipedia style), we have: $R = kG$, where $0<k<n$ is a nonce and $G$ is the generator point. $e = H(R \| M) \bmod n$, where $H()$ is a hashing function and $M$ is the ...
0
votes
0answers
38 views

Discrete Logarithm within DH exchange - finding out A and B secret number [duplicate]

How would i find out Alices or Bobs private number from the details exchanged in public. prime - g = 7 primitive root - n = 3 Alice - A = 3 Bob - B = 4 The details visible in public exchange are: ...
2
votes
1answer
42 views

Embedding POW in an EC public key

I have an application where it would be advantageous for an attacker to have to spend a long time generating public keys. To do this, I require that the hash of the public key be less than a certain ...
3
votes
1answer
82 views

What's the Error in This Birthday-Problem Estimation?

Theorem: Choose $Q$ random natural numbers in the set $\{1,2, \dots, M\}.$ The probability of getting at least one collision is $$P_C(Q) = 1 - \frac{M - (Q - 1)}{M} P_{\neg C}(Q-1).$$ Notation: By ...
8
votes
2answers
513 views

Geometric interpretation of an Edwards curve

Addition on an elliptic curve in Weierstrass form (over the rationals) is typically depicted with the following figure: (Image CC SA 3.0 https://en.wikipedia.org/wiki/File:ECClines.svg) To add two ...
4
votes
1answer
76 views

Simple explanation of weak one way function

I find difficult to understand what a weak one way function is. From textbooks: $\exists$ poly $Q$, $\forall$ PPT $\mathcal{A}$ such that: $$\Pr[x\leftarrow\{0,1\}^n; y=f(x); \mathcal{A}(1^n, f(x))=...
0
votes
0answers
24 views

What is $n_0$ in the definition of neglibible? [duplicate]

In a lecture, I have seen the following: Negligible Function: a function $f(n)$ is negligible if $\forall$ polyn. $p \;\exists n_0 \text{ s.t. }\forall n>n_o\; f(n) < 1/p(n)$ What is exactly ...
1
vote
1answer
48 views

How Secure is gpg Command Using Symmetric AES-256 From Being Cracked

How secure is any data encrypted using the following command: gpg -o *encrypted_output_file_name* --symmetric --cipher-algo AES256 *file_to_be_encrypted* ...
0
votes
1answer
110 views

What's the best block cipher mode of operation for RSA?

I know that you should never use RSA with any block cipher mode of operation, but theoretically, what's the best block cipher mode (safest) we can use with RSA encryption - without adding any kind of ...
-1
votes
1answer
33 views

find additive inverse of modular arithmetic [closed]

For a set to be called as a ring, it should have the following properties closed commutative associative Identity existence Inverse existence but how is Z7 a ring, as there aren't any inverse ...
0
votes
0answers
29 views

What choices of $a$ and $b$ of the affine cipher lead to proper encryption functions [duplicate]

Suppose I consider the affine cipher defined by $E(x) = ax + b \bmod n$ on the standard alphabet of 26 letters. Which choices of $a$ and $b$ lead to proper encryption functions? Using the ...
0
votes
0answers
47 views

Verifying valid public key and finding private key? [duplicate]

A naive user of RSA has announced the public key $n = 2903239, e = 5$. Eve has worked out that $n = 1237×2347$. Verify that the public key is valid and explain why the private key is $d = 2319725$. [...
2
votes
1answer
57 views

How to compare the order of elements in cyclic groups?

In a cyclic group with randomly looking behavior like the one used in secp256k1, is there any known efficient algorithm to compare the order of two randomly given elements $P_1$ and $P_2$ and find out ...
1
vote
2answers
52 views

Why can´t an attacker find the key if he has the plain text, the IV and the ciphertext? [duplicate]

I am reading a book about web security and they are now talking about AES CBC. After reading the chapter I was wondering, can an attacker compute my secret key if he has access to the IV, the plain ...
0
votes
0answers
71 views

Computing a probability

Let $(w_1,\cdots,w_l) \in (\{0,1\}^\lambda)^l$, and $r_1,\cdots,r_l $ are chosed as uniformly random from $Z^*_q$ such that $r_1+\cdots+r_l=0$ and $q$ is a large prime number. Also, Let $F$is a ...
1
vote
1answer
37 views

Key, plaintext block and ciphertext block permutations question

Question: If a cipher’s key size is $k$ bits and its block size is $b$ bits, how many possible keys are there, how many possible plaintext blocks are there, and how many possible ciphertext blocks are ...
17
votes
4answers
4k views

Using Tweets as a Random seed

I would like to start by saying I know nothing about Cryptography and was reading up on how to choose a random seed and this link is something that I found. What I basically understood that the seed ...
2
votes
1answer
97 views

What is the point at infinity on secp256k1 and how to calculate it?

I hear that there should be a point at infinity on secp256k1. I wounder how to calculate it and what does it even mean. I tried to calculate it as $P_{inf}=P+(-P)$ but this gives different results for ...
1
vote
1answer
37 views

With AES-GCM, may I use multiple tags per key?

In my implementation of AES-GCM, the key might change only once per minute. However, I wish to calculate a new tag every 6us, to reduce latency (since you have to buffer up a GCM "packet" before ...
2
votes
0answers
84 views

How should we assess the quality of steganography?

I am asking this question instead of extending the discussion of another question (Perfect Steganography). I did try starting a chat room (https://chat.stackexchange.com/rooms/87636/perfect-...
0
votes
0answers
4 views

Fail to Sign/Verify signinature in C# [migrated]

I am trying to use the .Net RSA functions to sign a Hash, but when i try to Sign the hash and then verify the Signed string it turns out false... Is this the wrong place to ask? (Is this more of a ...
0
votes
0answers
23 views

In AES is 0x11b is the specified field generator? [duplicate]

As I know all arithmetic operations in AES are done over $GF(2^8)$ so I want to know which field generator AES uses? is it 0x11B? and choosing another field generator would it give a different results?...
2
votes
1answer
70 views

One-round feistel network (DES) attack

I can't find out how to break 1 round of feistel network (obtaining the key). I understand why this equation takes place: $R_1 \oplus L_0 = f(R_0, k_1)$ EDIT: The function f looks like this: But ...
4
votes
1answer
60 views

Does Elliptic Curve Integrated Encryption Scheme (ECIES) provide IND-CCA2 security?

I am looking for a faster alternative to RSA with OAEP as a IND-CCA2 public key scheme. Elliptic Curve Integrated Encryption Scheme might be a candidate, but I am not sure if it provides IND-CCA2 ...
3
votes
2answers
480 views

Can AES be used with a static key?

I am making an embedded system for a project that uses AES. As I cannot accommodate key generation (hardware constraints) I am using a static key. I can use another small algorithm to create dynamism ...
0
votes
2answers
88 views

How to create a private key using $n,e,d,p,q$ where $n$ is prime

Someone has incorrectly created a public/private key pair where $N$ (modulus) is a prime number. This makes $p$ and $q$ trivial as they they are $n$ and $1$. $d$ is solved from $d \cdot e = \bmod (...

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